A method for calculating pole arc of switched reluctance motor based on scalar magnetic potential function method

Abstract

A method for calculating the pole arc of a switched reluctance motor based on a scalar magnetic potential function method relates to the field of switched reluctance motors. The present invention is to solve the problem that the existing methods for designing the rotor main pole arc of a switched reluctance motor cannot meet the requirements. The method for calculating the pole arc of a switched reluctance motor based on a scalar magnetic potential function method described in the present invention first establishes a scalar magnetic potential boundary condition at the location of the pole arc; then, within the scalar magnetic potential boundary condition, an expression for the scalar magnetic potential within the air gap magnetic field is established; finally, an expression for the motor pole arc radius is established based on the scalar magnetic potential to obtain the pole arc of the switched reluctance motor.

Description

Technical Field

[0001] The invention belongs to the field of switched reluctance motors, and in particular relates to the calculation of pole arcs of switched reluctance motors. Background Art

[0002] Switched reluctance motors are widely used in electric vehicle drives, general industry, household appliances, textile machinery and other industrial fields because of their simple structure, wide speed regulation range and reliable system operation. At present, the rotor pole arc design method and optimization method of switched reluctance motors are very mature, but in the analysis of motor operation performance, the torque pulsation and vibration noise of switched reluctance motors are still problems. Therefore, it is necessary to propose a new design method for the rotor main pole arc of switched reluctance motors. The rotor main pole arc structure determines the shape of the stator and rotor air gaps, and the motor air gap structure determines the motor's operating performance. Therefore, the design of the main pole arc structure plays a very important role in the design of switched reluctance motors.

[0003] At present, the design methods for the rotor main pole arc of the switched reluctance motor include finite element numerical method and analytical method. Although the multi-objective optimization calculation of structural parameters by finite element is more accurate, it is still necessary to repeatedly modify the physical model when studying certain problems, and simulation often takes a lot of time. The analytical method is simpler, easy to program, and has a fast solution speed, but it is only suitable for studying such problems under the condition of meeting a certain accuracy. Summary of the invention

[0004] The present invention aims to solve the problem that the existing rotor main pole arc design methods of the switched reluctance motor cannot meet the demand, and now provides a switched reluctance motor pole arc calculation method based on a scalar magnetic potential function method.

[0005] A method for calculating the pole arc of a switched reluctance motor based on a scalar magnetic potential function method, wherein the method for calculating the pole arc of a switched reluctance motor is:

[0006] First, the scalar magnetic potential boundary conditions at the location of the pole arc are established;

[0007] Then, the expression of scalar magnetic potential in the air gap magnetic field is established within the scalar magnetic potential boundary condition;

[0008] Finally, the motor pole arc radius expression is established according to the scalar magnetic potential to obtain the switched reluctance motor pole arc.

[0009] Furthermore, in the polar coordinate system, it is assumed that the rotor surface is smooth, the rotor outer diameter is R1, the stator inner diameter is R2, the number of pole pairs is P, and the magnetic permeability of the stator and rotor cores is positive infinity.

[0010] The scalar magnetic potential boundary conditions are: the magnetic potential on the rotor main pole surface is 0, the magnetic potential on the armature surface is Ω0, the air gap magnetic field on the main pole surface is sinusoidally distributed, and the radial component of the magnetic field on the main pole surface is Br =B f cosΡθ,

[0011] Among them, θ is the position angle of each point on the armature surface in the polar coordinate system, B f is the radial component of the fundamental wave of the air gap magnetic field.

[0012] Furthermore, the expression of the scalar magnetic potential Ω in the air gap magnetic field is:

[0013]

[0014] Among them, μ0 is the vacuum permeability and R is the motor pole arc radius.

[0015] Furthermore, the expression of the motor pole arc radius R is:

[0016]

[0017] Furthermore, there is an air gap between the inner surface of the stator and the outer surface of the motor pole arc, and the air gap is an uneven air gap, with the smallest air gap in the middle of the motor pole arc and the largest air gap at both ends.

[0018] Furthermore, the expression of the air gap δ is:

[0019] δ=R2-R.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention combines the actual motor stator and rotor structural characteristics to establish a rotor pole arc model, which can optimize the air gap flux density and effectively reduce the harmonic content of the air gap flux density. The present invention is applicable to switched reluctance motors with any pole slot combination and has important engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a flow chart of a method for calculating pole arc of a switched reluctance motor based on a scalar magnetic potential function method;

[0023] Figure 2 This is the air gap modeling diagram considering the influence of the actual structure of the stator and rotor;

[0024] Figure 3 This is the model diagram of the switched reluctance motor;

[0025] Figure 4 This is the rotor pole arc structure diagram of the switched reluctance motor;

[0026] Figure 5 A comparison diagram of the electromagnetic torque waveforms of the motor of the prior art and the present application;

[0027] Figure 6 A comparison diagram of the air gap flux density waveforms of the motor of the prior art and the present application;

[0028] Figure 7 It is a comparison chart of the harmonic content of the air gap magnetic flux Fourier decomposition of the motor of the prior art and the motor of the present application. DETAILED DESCRIPTION

[0029] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0030] Specific implementation method one: The scalar magnetic potential function method is a magnetic potential calculation method based on Ampere's loop law, with position change as the intermediate variable. The calculation is simple, fast, and accurate enough to meet engineering needs. For the switched reluctance motor, how to establish a regional mathematical model suitable for the scalar magnetic potential function method is the key to studying such problems. At the same time, for the accuracy of the calculation, how to fully consider the actual structure of the motor stator and rotor is also one of the difficulties in this field. To this end, this implementation method provides a switched reluctance motor pole arc calculation method based on the scalar magnetic potential function method, referring to Figure 1 Specifically describing this embodiment, a method for calculating the pole arc of a switched reluctance motor based on a scalar magnetic potential function method described in this embodiment is as follows:

[0031] 1. Establish the scalar magnetic potential boundary conditions at the location of the pole arc. Specifically, first select the polar coordinate system. When the switched reluctance motor is running, there is only the armature magnetic field. At this time, the magnetic field in the air gap is a constant irrotational magnetic field, and the scalar magnetic potential Ω in the air gap satisfies the Laplace equation. Assume that the rotor surface is smooth, the rotor outer diameter is R1, the stator inner diameter is R2, the number of pole pairs is P, and the magnetic permeability of the stator and rotor cores is positive infinity. Then the scalar magnetic potential boundary conditions are:

[0032] The magnetic potential on the rotor main pole surface is 0, the magnetic potential on the armature surface is Ω0, the air gap magnetic field on the main pole surface is sinusoidally distributed, and the radial component of the magnetic field on the main pole surface is B r =B f cosΡθ, where θ is the position angle of each point on the armature surface in the polar coordinate system, B f is the radial component of the fundamental wave of the air gap magnetic field.

[0033] 2. In polar coordinates, the scalar magnetic potential Ω in the air gap magnetic field satisfies the general solution of the Laplace equation. According to the scalar magnetic potential boundary conditions on the rotor main pole surface, the expression of the scalar magnetic potential Ω in the air gap magnetic field can be derived:

[0034]

[0035] Among them, μ0 is the vacuum permeability and R is the motor pole arc radius.

[0036] 3. Establish the expression of motor pole arc radius R based on scalar magnetic potential:

[0037]

[0038] Finally, the pole arc of the switched reluctance motor is obtained using the above formula.

[0039] Furthermore, in this embodiment, there is an air gap between the inner surface of the stator and the outer surface of the motor pole arc, and the air gap is an uneven air gap, with the smallest air gap in the middle of the motor pole arc and the largest air gap at both ends. The uneven air gap optimizes the harmonic magnetic field in the air gap magnetic field, and the amplitude of the harmonic magnetic field will be significantly reduced when passing through the air gap.

[0040] The expression of air gap δ is: δ = R2-R.

[0041] This implementation improves the traditional switched reluctance motor rotor pole arc, optimizes the motor stator and rotor air gap, reduces the harmonic content of the motor air gap magnetic flux density, and effectively reduces the torque pulsation and vibration noise during operation. It is suitable for switched reluctance motors with any pole-slot combination.

[0042] This implementation combines the motor stator structure, rotor structure and air gap scalar magnetic potential distribution characteristics, and comprehensively considers the pole arc design with the motor torque pulsation and air gap magnetic flux density, so that the new pole arc design algorithm can focus on optimizing the motor torque pulsation and air gap magnetic flux density. Specific embodiments

[0044] The pole arc calculation method of the switched reluctance motor of the present invention is described in detail below by taking a 12-slot 8-pole switched reluctance motor as an object.

[0045] Table 1 Basic parameters of motor

[0046] Stator inner diameter 120mm Number of stator slots 12 Rotor outer diameter 117.6mm Number of poles 4 Air gap length 2.4mm Stator tooth width 17.84mm Axial length 141mm Rotor pole shoe width 22.04mm

[0047] Step 1:

[0048] According to the basic parameters of the motor in Table 1, the scalar magnetic potential boundary conditions at the location of the pole arc can be obtained as follows:

[0049] The rotor outer diameter R1 = 117.6 mm, the stator inner diameter R2 = 120 mm, the magnetic potential on the rotor main pole surface is 0, the magnetic potential on the armature surface is Ω0, and the radial component of the magnetic field on the main pole surface is B r =B f cosΡθ,

[0050] Step 2:

[0051] According to the above boundary conditions, the expression of the scalar magnetic potential in the air gap magnetic field can be obtained as:

[0052]

[0053] Step 3:

[0054] The expression of the motor pole arc radius R is:

[0055]

[0056] Step 4:

[0057] The expression of air gap δ is:

[0058]

[0059] The air gap model simulated by Matlab software is shown in Figure 2 The finite element numerical method is used to apply this method to a 12-pole 8-slot switched reluctance motor. The switched reluctance motor model is shown in Figure 3 As shown. The rotor pole arc obtained according to the new pole arc design method is as follows Figure 4 As shown, the outer surface of the pole arc and the inner surface of the stator form unequal air gaps, which helps to weaken the air gap harmonic flux density. Figure 5 This is a comparison diagram of the motor torque waveform of the prior art and the present application, from Figure 5 It can be found that the torque waveform obtained by the present application is relatively smooth, and the maximum torque value is significantly reduced. The rated torque of the prior art is 25N.m, the maximum torque value is 31.2Nm, and the minimum torque value is 13.8Nm. The torque pulsation of the prior art is calculated to be 68%; the maximum torque of the present application is 28.2Nm, and the minimum torque value is 13.6Nm. The torque pulsation of the present application is calculated to be 58.4%, which is effectively reduced by 10%. Figure 6 The air gap magnetic flux waveforms under the two schemes are shown in FIG. 1 . It can be seen that the air gap magnetic flux waveform under the present application is smoother. Figure 7 The air gap magnetic flux was decomposed by Fourier transform. Figure 7 It can be seen that the fundamental magnetic flux density of the switched reluctance motor under the present application is effectively increased, and the remaining harmonic magnetic flux densities are significantly reduced. As shown in the motor torque waveform and the air gap magnetic flux waveform, the harmonic magnetic flux density is effectively reduced and the waveform is smoother.

[0060] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that the features described in conjunction with a single embodiment may be used in other described embodiments.

Claims

1. A method for calculating the pole arc of a switched reluctance motor based on a scalar magnetic potential function method, characterized in that: The pole arc calculation method of the switched reluctance motor is: First, the scalar magnetic potential boundary conditions at the location of the pole arc are established; Then, the expression of scalar magnetic potential in the air gap magnetic field is established within the scalar magnetic potential boundary condition; Finally, the motor pole arc radius expression is established according to the scalar magnetic potential, and the pole arc of the switched reluctance motor is obtained; In the polar coordinate system, assume that the rotor surface is smooth and the outer diameter of the rotor is , the inner diameter of the stator is , the pole pair number is , the magnetic permeability of the stator and rotor cores is positive infinity, The scalar magnetic potential boundary conditions are: the magnetic potential on the rotor main pole surface is 0, and the magnetic potential on the armature surface is , the air gap magnetic field on the main pole surface is sinusoidally distributed, and the radial component of the magnetic field on the main pole surface is , in, is the position angle of each location on the armature surface in the polar coordinate system, is the radial component of the fundamental wave of the air gap magnetic field; Scalar magnetic potential in the air gap magnetic field The expression is: ， in, is the vacuum permeability, is the motor pole arc radius; Motor pole arc radius The expression is: ； There is an air gap between the inner surface of the stator and the outer surface of the motor pole arc. The air gap is an uneven air gap. The air gap in the middle of the motor pole arc is the smallest, and the air gap at both ends is the largest.

2. The method for calculating the pole arc of a switched reluctance motor based on a scalar magnetic potential function method according to claim 1, characterized in that: Air Gap The expression is: ， in, is the inner diameter of the stator, is the motor pole arc radius.

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